Thermal neutron detectors and system using the same

Abstract

A solid state thermal neutron detector. The improved detector for particularly high temperature applications of thermal neutron flux determination, employs a differential thermocouple unit having the hot junction positioned within a cylindrical pellet or compact of uranium dioxide (UO.sub.2) partially enriched in uranium-235. The cold junction is positioned within a cylindrical pellet or compact of depleted uranium dioxide, this second pellet having the identical mass as the first. The uranium-containing pellets are spaced apart by a cylindrical pellet of a high temperature insulator, such as MgO or aluminum oxide (Al.sub.2 O.sub.3). Similar insulator pellets are positioned outwardly from the uranium-containing pellets to prevent heat loss. The entire assembly is enclosed in a cylindrical sheath of a material resistant to the environment of the detector, with this sheath being radially swaged upon the pellets to achieve intimate thermal contact between the pellets and the differential thermocouple. In one embodiment, a plurality of differential thermocouples are inserted in alternating pellets. In a preferred embodiment, a heater unit is included with a high temperature portion proximate the hot junction and a lower temperature portion proximate the cold junction. The thermocouple is connected to appropriate measuring circuits and monitor, and the heater is connected to a regulated and adjustable heater supply. Provision for axial movement of the detector unit and for determining absolute temperatures are discussed.